One of the weakest components of modern transient simulation software is the transformer model. Many opportunities exist to improve the simulation of its complicated behaviors, which include magnetic saturation of the core, frequency-dependency, capacitive coupling, and topologically correctness of core and coil structure. This paper presents a review of transformer models for simulation of low- and mid-frequency transients. Salient points of key references are presented and discussed in order to give an accessible overview of development, implementation and limitations of the most useful models proposed to date. Techniques for representation of the most important behaviors are examined, with the intent of providing the needed foundation for continued development and improvement of transformer models.

Transformer modeling for low- and mid-frequency transients - a review

Transformer modeling for transient simulations has many challenges because of nonlinear and frequency-dependent behavior. Some of the model parameters are relatively easy to obtain from standard factory tests. Other parameters can only be obtained from special tests or by estimation. This paper provides guidelines for the estimation of transformer model parameters for low- and mid-frequency transient simulations. The paper also discusses several transformer models that can be used for transient simulation.

Parameter determination for modeling system transients-Part III: Transformers

Overhead line parameters are calculated, taking into account the length of the line and the frequency range of the transient to be simulated. Depending on the frequency range and the origin of the transient, several parts of the line (phase conductors, shield wires, towers or poles, footing impedances, insulators) have to be included in the model. In all cases, the most important part is phase conductors. This paper describes an input requirement for obtaining electric overhead line parameters and investigates the sensitivity of these parameters with respect to some input data. The aim is to conclude on the accuracy with which input values must be specified. An illustrative example is included to support the main conclusions.

Parameter determination for modeling system transients-Part I: overhead lines

Catastrophic equipment failures continue to occur today due to ferroresonance even though this phenomenon has been extensively studied over the past ninety years. This paper is concerned with describing practical examples of ferroresonance in a high voltage transmission system. Methods of mitigating ferroresonance are discussed.

Examples of ferroresonance in a high voltage power system

The magnetic hysteresis phenomenon plays an important role in the ferroresonance behavior of a transformer. However, most existing transformer models for the analysis of the ferroresonance phenomenon either ignore the hysteresis effects or represent it based on the hysteresis major loop and scale it for lower current levels. Such a modeling approach does not reflect the actual physical behavior of the magnetic core with respect to the ferroresonance phenomenon. This paper, based on Preisach theory, introduces an accurate model of hysteretic inductor to represent a single-phase transformer for the investigation of the ferroresonance phenomenon. Based on the developed model, time-domain simulation studies show that even in the case of a single-phase transformer where no magnetic coupling exists between the three-phases, all known types of ferroresonance, including fundamental, sub-harmonic, quasi-periodic and chaotic modes, may occur. The effects of hysteresis and its initial conditions, grading capacitors and transformer winding capacitance on occurrence of ferroresonance and its change of mode are also discussed

Analysis of Ferroresonance Modes in Power Transformers Using Preisach-Type Hysteretic Magnetizing Inductance

The ability to predict or confirm ferroresonance depends primarily on the correctness of the transformer model used by the computer simulation. Ferroresonance is introduced and a general modeling approach is given. An overview of available literature and contributors to this area is provided. A simple ease of ferroresonance in a single phase transformer is used to illustrate this "phenomenon". Three phase transformer core structures are discussed. Ferroresonance in three phase grounded-wye distribution systems is described and illustrated with waveform data obtained from laboratory simulations. Representation of the study zone is discussed, modeling techniques are presented, and implementation suggestions are made. Three case studies are presented. Transformer representation is critical to performing a valid simulation. The direction of ongoing research is discussed, and the reader is advised to monitor the literature for ongoing rapid improvements in transformer modeling techniques.

Modeling and analysis guidelines for slow transients. III. The study of ferroresonance

The first part of this three-part report explains the objectives of the task force and the scope of its report (1995). The first part also provides modelling guidelines for the investigation of small-signal torsional oscillations, large-signal shaft transient stresses, turbine-blade vibrations, and fast bus transfer based on the use of digital computer time-domain simulation methods. This paper provides modelling guidelines for the analysis of controller interactions, harmonic interactions, and resonance phenomena in power systems. Sample test systems and typical time-domain simulation results for each phenomenon are also provided.

D.A. Woodford

Papers

Modeling and analysis guidelines for slow transients. III. The study of ferroresonance

Modelling and analysis guidelines for slow transients. II. Controller interactions; harmonic interactions